In recent years, development of organic light-emitting devices such as organic electroluminescence (EL) display panels and organic EL lighting devices has flourished. For example, an organic light-emitting device includes a thin film transistor (TFT) substrate, an anode, a light-emitting layer, and a cathode. An organic EL element further includes, as necessary, a hole injection layer, a hole transport layer, an electron injection layer, an electron transport layer, a sealing layer, and the like. An organic EL display panel includes a plurality of subpixels that are arranged two-dimensionally along a main surface of a substrate. Each subpixel has a structure in which an anode, a hole injection layer, a hole transport layer, an organic light-emitting layer, an electron transport layer, and a cathode are stacked in this order on the substrate.
In some active matrix driven organic EL display panels, a plurality of independent electrodes corresponding one-to-one to a plurality of pixels are formed as anodes, and a common electrode that is continuous over the plurality of pixels is formed as a cathode. When the cathode is continuous over a plurality of pixels as described above, voltages are applied from a peripheral portion of the cathode. As a result, a central portion of the cathode receives a lower voltage than a voltage that portions closer to the peripheral portion receive, due to electrical resistance of the cathode itself. Further, in such an organic EL display panel, the distance from the peripheral portion of the common electrode to one pixel differs from the distance from the peripheral portion of the common electrode to another pixel. Due to this structure, voltage between the cathode and the anode in one pixel differs from voltage between the cathode and the anode in another pixel. This results in unevenness of luminance of the organic EL display panel. Such voltage differences are especially salient in large-size organic EL display panels.
In response to this, Patent Literature 1 discloses a technology for reducing differences in voltage between pixels by disposing wiring on the substrate and electrically connecting the wiring and the upper electrode. In many cases, such an electrical connection is achieved by putting the wiring and the cathode in direct contact.
Further, research and development are being carried out on a layer of an organic material doped with an alkali metal and an alkaline earth metal, which have a low work function, as an electron transport layer. It is known that an excellent electron injection property can be achieved by adopting such an electron transport layer.
Alkali metals and alkaline earth metals, which have a low work function, have a characteristic of easily reacting to impurities such as moisture and oxygen. This characteristic is likely to cause degradation of functional layers that contain an alkali metal or an alkaline earth metal when such impurities are existent. Due to this, an organic EL element including such a functional layer suffers an adverse effect such as degradation of light emission efficiency, shortening of light-emitting lifetime, and degradation of storage stability. Also, contact between impurities and a cathode made of a metal causes corrosion and degradation of the cathode, and an organic EL element including such a cathode can suffer the same adverse effects as described above. Specifically, when a light-emitting layer, a hole injection layer, a hole transport layer, a bank and the like are formed through a wet process, impurities (moisture, oxygen) may remain on surfaces of these layers or within these layers. These impurities can cause degradation of the metal forming the cathode and the alkali metal or the alkaline earth metal in the functional layer.
In response to this, Patent Literature 2 discloses a technology of interposing an intermediate layer made of a fluoride of an alkali metal or a fluoride of an alkaline earth metal between a light-emitting layer and an organic functional layer.